The invention relates to an x-ray diagnostic installation comprising an x-ray image intensifier television chain, wherein a television camera is coupled, by means of an optical system with a base lens and a camera lens, to the x-ray image intensifer, in the parallel ray path of which a mirror is disposed which couples a portion of the luminous flux to a light detector.
In the German LP 16 14 683 and in the corresponding British Pat. No. 1,237,007, an x-ray diagnostic installation of the type initially cited is described wherein an x-ray image intensifier converts an x-ray image into visible image. By means of a lens system with a base lens and a camera lens the output image of the x-ray image intensifier is transmitted to a television camera. A portion of the light emanating from the output fluorescent screen of the x-ray image intensifier is projected, via a small mirror, onto the photocathode of a photomultiplier whose output signal is employed for the control of the high voltage generator of the x-ray diagnostic installation. A desired dominant measurement field is established through the mechanical conditions. A signal representing the image contents within the dominant field is obtained by means of the photomultiplier. A subsequent alteration of the dominant measuring field can only be attained with difficulty.
It is furthermore known from the German LP 20 32 780 to employ a television pickup tube as a light detector for a radiographic control system. For this purpose the cyclically varying deflection signals for effecting cyclical deflection of the scanning beam are disconnected (or switched off) and the scanning beam is enlarged to correspond to the desired dominant field size. Through application of steady deflection signals any desired position of the dominant field can be attained. Such a measuring and control system is not suitable for rendering possible a varying weighting of individual measuring fields pertaining to the dominant field, and, in the case of indirect radiographs, it is not suitable for very short exposure times.